Astrophotography

Star Trails/Astro

Astro Essentials

Here are some tools that are necessary for being successful while shooting astrophotography

Tripod

Even with great Vibration Reduction tech in your lenses, you can only hold it so still for so long. Using a tripod will make all the difference while shooting at night. There is no way around it.

Headlamp

Every time I go out and shoot at night, I bring my headlamp. I have a Black Diamond Storm and its my favorite lamp yet. It has a flood light, spot light, both combined, red LED and a green LED. The RED allows me to keep my night vision and operate camera settings without blinding myself. I can walk around behind my camera while it is exposing and red will not blow out the shot, unlike the bright white light. The white light allows for light painting when you want to be creative. This is limited to the imagination, but doesn’t always look good and should be well planned and practiced. It is fun to experiment and know what your camera will pick up.

Remote Release

This is obvious for triggering the exposures without touching the camera, causing unnecessary vibrations and camera blur. Also, if you are wanting to expose longer than 30 seconds, you must use a remote release to trigger it. My wireless remote has a single button. When I shoot long exposures, I first set my camera to “mirror up mode” and then use the remote to trigger the mirror. This takes one press. Another press triggers the exposure. If it’s set to 30 seconds, it will complete that exposure and be done. If the camera is in “bulb” mode then I press the remote, trigger the mirror, and then press and hold the button to start the exposure. Once the exposure is locked and active, one more press will end the exposure, thus allowing you to shoot longer than 30 seconds.

Watch

When I am out at night, the temperature drops significantly in the mountains, and sometimes will render my phone useless. If you are relying on your phone as a timer, it could die halfway through and you won’t know how long your exposure will be, if you were timing it to begin with. Instead, I prefer to use a wristwatch and set a timer on it. This never lets me down and can handle the colder temperatures. Paying attention to exposure length is critical to not overexpose and to stay consistent.

Lenses

Ideally you want as fast as a lens as possible. F-numbers tell us how fast a lens is. The smaller the number (ie: f/1.8) the more light the lens absorbs and the faster shutter speed can be used. f/2.8 is a great start for Astrophotography. One of my favorite lenses for night photography is the Nikon 20mm f/1.8G. It captures a lot of light and can allow lower ISO. f/4 is a little on the small side (aperture is smaller with larger number) and lets in less light. To make up for this one would increase ISO or lengthen shutter speed to make up for lost light. This can be a pain if you are photographing star points because you want a short shutter speed to get sharp stars. For star trails, longer shutter speeds are acceptable and you can get away with a higher f-number. Wider is usually better when capturing the night sky. 24mm is on the narrower end of the spectrum but still a great focal length. As you approach 20mm and below, the more you are able to capture. Nikon makes a 24mm f/2.8 lens that is older and more affordable if you are just getting into night photography.

Star Trails Shapes

Where you point your camera will determine how your star trails appear. I prefer to aim my camera to the North (in the northern hemisphere) to get circular star trails. If you are in the southern hemisphere you want to aim south towards the south pole to get circular stars. If you aim east or west, they are more lines than circles. They can still look just as great if done properly. Bring a compass or use the one on your smartphone while setting up your composition!

Exposure Lengths

This depends on what your goals are:

Static Star Points - requires short exposures, depends on the focal length used, they are all different.

Star Trails - longer shutter speeds, ideally you want a minimum of a one hour exposure.

When shooting points, you want no movement at all. You can use an app to calculate the exact exposure time, PhotoPills. They provide precise exposure length for your focal length. For example, my 20mm f/1.8 set at f/1.8 on my Nikon D810 (36MP taken into consideration by app) requires a shutter speed of only 4.91s. The old 500 rule would have had me around 20 seconds or just under that. Even with the old 500 rule, there is minimal motion blur of the stars, which is undesirable. Of course most people will not notice this movement, especially if not printed large. If you shoot with a 20mm lens, you can get away with 15s shutter speed and get acceptable shots. However, for those wanting to be precise and/or wanting to make large prints, you want to have a much shorter shutter speed as discussed above. Check online or use PhotoPills to get yours dialed in.

Capturing star trails becomes a little more flexible with shutter speed. You can shoot at your cameras max shutter speed (usually 30 seconds) and take a lot of photos and blend them together in Photoshop. You may also put your camera into “bulb” mode and do single exposures as long as your battery can last. There are some caveats to that, though.

Interval Timer

One of the cleanest ways to get star trails is to shoot using your cameras “interval timer shooting” setting. This allows the camera to shoot frames, at your desired sequence and timing, all automatically. For Nikon users this falls under the “shooting menu”. In this menu, your options become:

Start (may be greyed out, get back to this in a minute)

Start options

Interval No. of intervals x shots/interval

Exposure Smoothing

To be clear, this is all done in camera. There are also external intervalometer remotes that can control these settings and even additional settings not available in the camera. Back on topic.

Start Settings

When I set my set my start options, it is always set to “now” because I am doing it on the spot. If your “start” option is greyed out and you are unable to begin the sequence, check to make sure “live view” isn’t on. Turn that off and then re-access the menu and the “start” option should be clickable.

Interval Settings

My interval settings are as follow: 00:00’33” which means 33 seconds between shots. There is a specific reason for this. If I am shooting 30 second exposures, there is delay between the shutter releasing and mirror going up for the next frame (provided you are using a DSLR). This takes my D810 that few seconds in order to not skip any frames. If you set your interval to 32” you are going to be losing about half of your frames or so and wonder why when you set your camera to take 300 photos and it only took 150+/-. Why not set it to 34” and give it even more time? The longer between each shot, the larger the gap in the star trails. At 33” it is unnoticeable unless zoomed into 500% or something ridiculous like that. The more seconds you add between each frame, the funkier the gap will become and the trails won’t be cohesive.

Depending on your level of commitment, you can figure out how long of an exposure you want to go for. I feel an hour minimum, is a good starting point. You could get away with 30 minutes, but the longer length of the trails will appear more dramatic. This also depends on how much sky you have in your frame. The more sky you include, the longer the exposures should be. If you only have 10% sky, you can make a half hour exposure look alright.

Once you get your first few trails down and want to go for longer, you can start capturing up to 3 or 4 hour exposures. This will sometimes fill the entire sky with stars, leaving little to no room of empty space. This is ultra dramatic and requires a lot of patience and planning.

All this means, is that the camera is going to capture 300 photos and only 1 sequence of this = 300 total frames

This is equivalent to a 2.5 hour exposure when combined together in photoshop (100 frames x 1 = 100 total frames = 50 minute exposure - a good start!)

A benefit to using the interval timer is that if you get airplanes or satellites in your frame, you are easily able to remove it from that individual frame. This saves you from having to clone out 40 flying objects if you were to capture it in a single exposure. Also, you may be in an area where there are cars driving by, and their headlights may ruin a few of your images. You can delete these and have a minimal impact on your overall photo after they are combined. The more frames you have, the more flexible you can be with removing bad frames.

Another tip, interval sequences can be turned into a time-lapse! This is a two for one.

One last tip for shooting many photos in sequence for layering. If you are shooting RAW files, and layer up to 200+ shots, you might be looking at a file of over 25GB in size and this can take your computer hours to process, depending on your hardware, etc. Once you layer the shots and change the blend mode, you can flatten the image and it will be reduced to under 1GB, allowing you to further process the image and not tax your computer. But getting all of the files layered will take time and patience, especially when removing planes, satellites, etc. If you are wanting to attempt trails, you can start out using the lowest quality JPGs and then once you have everything dialed in, start making the change to shoot RAW. This will keep the massive file sizes down when layering in Photoshop.

Exposure Smoothing

Turn this on to help smooth the exposures in quickly changing light. This can help if the night starts out dark and then progressively becomes brighter with the moonrise. Leave off if you want to manually fix the brighter exposures in Lightroom or Photoshop.

Single Exposures

Capturing a single frame, long exposure shot is difficult and a single event can ruin the entire image, and waste hours of your time. Plus you have to be more careful with ISO, and long exposure noise. Long exposure noise happens when the sensor heats up during the exposure, leading to “hot pixels”. These pixels are red, green and blue spots that can show up in a few spots, or be all over the entire image, resulting in a ruined photograph. There are ways to fix these hot pixels in photoshop, or by creating your own “dark frames”.

Dark Frames

These are frames that are captured with the lens cap ON. Yes, you do want the cap ON so light doesn’t reach the sensor. You will expose for the same length of your original shot, and layer this frame on top of it, “subtracting” the “hot pixels” in photoshop. Sometimes one dark frame will not remove all of the hot pixels, therefore it’s recommended to take a few if you have enough time. In my experience, I have a hard time with dark frames. I even created a “master” dark frame consisting of multiple dark frames, layered together, to try and get any hot pixel that would show up but this was a failure on my part. Ambient temperature comes into play here as well and must be consistent while capturing dark frames. There are a lot of variables!

Photoshop Fixes

In photoshop, you can navigate to "Filter">Noise>"Dust and "Scratches

Set the numbers low and see what works best eliminating the hot pixels (zoom in to verify)

Using this technique can reduce the sharpness of the overall image and is not the best method

Long Exposure Noise Reduction

If you are trying a single long exposure, you can turn on a setting named “long exposure noise reduction” and this will automatically capture the “dark frames” for you. I’ve experimented with this a few times and find it to be actually pretty reliable. On the internet you will find a lot of people stating that dark frames are the only way to go and that you need to create them yourself and that the in-camera “long exposure noise reduction” does not work properly. This is the opposite of my experience and you can try this for yourself to see how it works. It isn’t always perfect, but you can clone out the few hot pixels that do remain if there are any.

When shooting with LENR (Long exposure noise reduction) turned on, the camera is going to capture the dark frame immediately after you finish your original shot. Lets say you take a 30 minute frame, as soon as this exposure ends, the camera will trigger the dark frame and begin the subtraction process for you. What this means is that your camera will be inoperable for an additional 30 minutes bringing you to a total of 1 hour. If you shoot a 1 hour exposure, your camera will be working for 2 hours. You do not need to have the lens cap on while the camera takes the dark frames, its smart enough to not let the light in, but to heat the sensor up, exposing the hot pixels. Though you may want to install the lens cap back on for glass protection purposes.

Battery Life

Single, Long Exposures drain the battery faster than shooting with the interval timer. If you only have 75% battery and you shoot an hour and a half exposure and drain your battery to 25%, the remaining battery life is not sufficient enough to complete the dark frame and will fail, thus leaving you with a photo covered in hot pixels.

There are external battery packs, and battery grips which extend the operating life of the camera. I recently invested in a used battery grip for my camera and got it at less than 25% of its original cost, shout out to eBay! This provides me with twice the battery life I would normally get. Flexibility is key and having the extra juice allows me to shoot long single exposures if I desire, or a ton of extra shots using the interval setting.

Before you start your sequence, you can take a few test shots using your current battery (or the one used at sunset) and then switch it for a fresh battery before starting the sequence. This will save you that little extra battery life in those times you really need it!

ISO

Don’t be scared to crank up your ISO a bit for night photography. Most of the time I will set mine to 3200 or greater, for both static and trails. Stacking is the best way to eliminate noise and get detail.

Stacking

Stacking refers to shooting the same scene, say a milky way shot, multiple times as fast as possible to get as little movement in the stars as possible and then layering these shots in photoshop to decrease the overall noise. This is something I am still working on and there are other programs that do it even better than photoshop, but I am learning these now. If you take 12 shots of the same scene at ISO 3200, the overall ISO when you layer them together would be much less, something like ISO 800 or even cleaner looking than that. In photoshop, you open the photos into layers, and then you “auto-align” and if that works properly, you select all of the photos and then change the blend mode to median and it will reduce the noise. This is for the people who are extremely picky and detail oriented and/or making large prints and want the most detail out of their camera.

Focusing

Even after doing astrophotography for over a year now, I still forget to set things properly. There are a lot of settings that go into astro and everything needs to be just right. Just the other day, I set up my camera interval timer and had it shooting something like 250 shots. I started the sequence and waited around on a big boulder while the camera did its thing. Once I saw the LED stopped flashing, the battery had died and it was time to replace it with the second to finish the sequence. I previewed a shot real quick and noticed that my autofocus settings were set to auto and not full manual focus. This resulted in the camera trying to focus in the pitch dark, which resulted in out of focus images and a ruined sequence. I wasted over an hour of my time sitting there while the camera took blurry shots the entire time. Always check your focus settings!

Using live view is a great way to make sure your stars are tack sharp. First you active live view, then you use your zoom keys (+) to zoom into the composition. If you are lucky enough you will be able to see at least one bright star or a planet. I suggest using manual focus here to dial things in. Once you have your focus sharp, you can zoom out or quit live view entirely and being shooting.

The distance between your foreground and camera and the sky are all different. Meaning that, you may potentially have to shoot a separate shot focusing on your foreground and then completing another entire sequence focused on the sky, so one is not blurry or out of focus.

Screen Display Brightness

While out in the pitch black, your screen brightness may feel overwhelming, especially once your eyes adjust. To counter this you can go into your menus and find the settings to turn the brightness down. This will also help you better expose your shots since darker shots won’t appear over-bright when the brightness is cranked up. Turning down the display will also save your battery life while previewing photos or looking through settings.

Foreground

Foreground can be equally important while shooting star trails or static star points. There are many ways to do this and it all depends on how much time you have at a particular location.

Let’s say you are out camping and arrive at a location before sunset. This allows you time to shoot sunset, and then wait around for “blue hour”. Blue hour is a great time to shoot your foreground and then wait for darkness to begin capturing the sky. This of course will be more work in the end, resulting in compositing the photo together in post-production (photoshop).

You may even capture the foreground during the day and then shoot the stars. This requires you to leave your tripod and camera in the exact same spot though so things will line up more easily in post production. Leaving the tripod in one spot limits your other shooting opportunities, but when put together correctly can have a special effect.

During the full moon, you are able to capture foreground objects quite easily due to the light intensity. This is another option under your belt for when you are out and arrive on location later than expected.

Example Settings

Some examples of how I’ve previously captured static stars or star trails

Static:

Manual Mode

Manual Focus

Lens: 20mm f/1.8G

Body: Nikon D810

ISO 3200-6400

Aperture f/2-2.8

Shutter Speed 10-20s

Trails:

Manual Mode

Manual Focus

Lens: 20mm f/1.8G Body:

Nikon D810 ISO 3200-5000

Aperture f/2.8

Shutter Speed 30s

Intervalometer set at 33” and 300x1 = 300 frames = 2.5 hour exposure

Exposure Smoothing: On

Hope these quick settings allow you to try them and experiment to see what works best for your particular set up. If you have any comments or questions, please feel free to reach out!